When performing optical analysis on specimens in liquid suspension, it is customary to discard the specimen after analysis. For rare cells, however, it is often desirable to preserve the liquid specimen for further testing or for use in further procedures. In certain procedures, it is desirable to select a specimen of a relatively small sample (less than 400 ul) from larger volumes (up to 100 ml), and it is likely that the volume of the specimen, which may be extracted from such a sample, is limited, making it especially important to avoid destruction of the specimen or any substantial part thereof. It is likewise important to avoid contamination of the specimen and to avoid conditions leading to deterioration of the specimen or impairment of analysis.
One cause of inconsistent optical analysis from sample to sample is a lack of uniform distribution of the magnetic particles and the magnetically labeled target components within the fluid sample due to gravitational forces. This pooling affect occurs when the sample is first placed into the cartridge chamber. Unless the chamber is perfectly horizontal, the magnetic particles, together with the magnetically labeled target components tend to settle toward the lower portions of the chamber. When the chamber is loaded in the vertical position, a preferred loading position, the magnetic particles and the magnetically labeled target components settle toward the distal portion of the chamber. Consequently, the magnetic particles and the magnetically labeled target components do not distribute uniformly across the optical window, causing the inability to perform optical analysis.
Another issue in the development of the cartridge and stopper is to provide a structure that is relatively inexpensive to manufacture (PCT/US02/04124), yet functions satisfactorily in preserving the sample. Construction, from two different plastic materials such as that described in the stopper component of the parent application, are expensive to manufacture and complicated in their construction. Since specimen samples are stored in a manner to prevent deterioration, there also is a need to maintain the locking feature so as to provide a proper seal against contamination and air. Thus, a stopper that would incorporate the benefits of a single elastomer composition together with a locking mechanism to minimize deterioration of the sample is needed.
In conjunction with a need to improve sample storage for optical analysis, there is a need to increase the ease and speed of manipulations of the cartridge. A better grasp on the cartridge would prevent unnecessary cartridge flexing that could allow air to enter the test chamber, and would provide more secure transfer of the cartridge from the loading position to the platform for analysis.